docs: def get(self, key, namespace=None):
          """Retrieve value for key."""
          # Short-circuit to reduce overhead.
          if not _CONFIG_OVERRIDE:
              return NO_VALUE
          full_key = generate_uppercase_key(key, namespace)
          logger.debug('Searching %s for %s', self, full_key)
          return get_key_from_envs(reversed(_CONFIG_OVERRIDE), full_key)